the aluminum piece is part of an electronics "project" box...approx 6 1/4" by 9 1/4" ...like you might find at Fry's or online...Radio Shack only has plastic ones (which was the original idea) but that would have required cutting and the aluminum one is a "clam shell" of two pieces

If you put a fan over that passive res, will it lower your temps by much?

In this pic I happen to have "Antec" Spot Fan behind my Pink Res.....
See the Screw and Bolt that's the Spot Fan minus the blue leds (I snipped off the LED lights carefully)mounted inside the 2x 5 1/4" bay that my IMON Ultra Bay is in. Pretty much hollow in there so I wired in the "Antec" Spot fan on "HIGH" to my AeroCool Easywatch which will auto regulate any fan you connect to it by using the Temp Sensors of the Easywatch. So I put the CASE temp sensor on the upper back side on my Pink Res...and the Antec Spot Fan behind blowing on it below the sensor! AeroCool does the rest... At idle the Fan is 2400 rpm or 25C on load it goes up to 2700 rmp to about 30C.